The present invention refers to and incorporates U.S. Pat. No. 4,457,252 issued Jul. 3, 1984 to Manske, Applicant of this patent application. The present invention relates to improvements of temperature indicators and provides for the detection of predetermined upper limit temperatures as well as predetermined lower limit temperatures, as disclosed in the U.S. Pat. No. 4,457,252. Particularly, this invention relates to a dual temperature indicator which provides an irreversible visual signal that it has been exposed to a temperature below a predetermined critical extreme, e.g. the freezing point of water, or exposed to a temperature above a predetermined critical extreme, e.g. 95 degrees Fahrenheit. The device of this invention is particularly useful for accompanying shipments of perishable or temperature sensitive products, such as pharmaceutical supplies or produce. The device provides a rapid and irreversible indicator so that the user is alerted to a past frozen or abnormally high temperature condition, even if that condition does not presently exist.
U.S. Pat. No. 4,457,252, CRITICAL TEMPERATURE INDICATOR, discloses an indicating device that visibly shows an irreversible color change when the temperature drops below a predetermined critical extreme. The art disclosed in the patent was exercised by 3M, and was manufactured and sold under the name "3M MonitorMark Coldside Indicator". Another device, "ColdMark Freeze Indicators" is manufactured and sold by IntroTech Inc. under license from 3M Co. However, these indicators only indicate low temperature extremes. Pharmaceutical customers, for example, use ColdMark Indicators to provide a visual indication if the temperature drops below a critical temperature, e.g. 32 degrees F., which inactivates their product. However, excessively high temperatures, e.g. 100 degrees F., may also inactivate their product. Therefore, in the warmer seasons users must utilize a different type of indicator which will provide an irreversible signal if the temperature goes above a predetermined critical level.
Despite the need for a dual critical temperature indicator device in the art, which gives a visible reading to the user of the occurrence of both temperature extremes, and which overcomes the limitations and problems of the prior art, none insofar as is known has been proposed or developed.
Accordingly, it is an object of the present invention to provide a device for the detection and recording of high and low temperature extremes, that can be attached to shipments of temperature sensitive goods and which will overcome prior art limitations and defects.